Issue 57

M. S ł owik, Frattura ed Integrità Strutturale, 57 (2021) 321-330; DOI: 10.3221/IGF-ESIS.57.23

can bring some doubts connecting with unsafe estimates for the structural members which are outside of empirical calibration. Therefore, the problem of shear capacity of members without transverse reinforcement is still attracted the interest of many researchers. Several works have been published recently, for instance [13-17]. The growing knowledge of shear behaviour in beams without stirrups brought the grounds for developing mechanical models of shear transfer mechanisms. Particularly, two theories, e.g. the Modified Compression Field Theory [18] and the Critical Shear Crack Theory [19], helped to work out the shear design concepts which were put into practice, for instance in the latest recommendation of International Federation for Structural Concrete – fib Model Code 2010 [20] and in a few national codes [21, 22]. It must be emphasized that these new design methods are dedicated to predict the shear capacity of typical slender beams. There are several potential shear transfer actions recognized by the researchers. Because the shear failure is affected by various factors, a theoretical description of shear transfer mechanisms is very complicated. The important parameter which influences the failure process in the beams is the ratio of longitudinal reinforcement. The influence of the longitudinal reinforcement ratio on the character of failure in flexural members has been analyzed in depth in [17]. Slightly reinforced concrete beams fail soon after appearing of a few flexural cracks and the failure process has a brittle character. In moderately reinforced concrete beams, a stable growth of several flexural cracks is usually observed and the full flexural capacity is reached. In higher reinforced concrete beams, the shear failure predominates due to shear forces and the propagation of inclined cracks. The shear failure often causes dangerous, brittle damage. However, the stable process of developing inclined cracks can also be observed and a relatively high shear capacity can be obtained in some kind of higher reinforced concrete beams [24]. The experimental results of shear capacity in reinforced concrete beams presented in professional literature show a big scatter. The question arises as to whether the shear capacity depends on the beam’s length and as to what contribution of the longitudinal reinforcement in the shear transfer is. When analyzing shear behaviour of longitudinally reinforced concrete beams without transverse reinforcement not only shear capacity should be of interest but also the progress of failure process should be examined. The development of cracks, the propagation of a critical crack and the stress distribution are of primary importance. Therefore, the author’s own experimental investigation was performed to analyze the failure process in longitudinally reinforced concrete beams. The experiment was focused on the observation of the cracks formation and propagation in the beams of a higher reinforcement ratio. Variable length of the beams and the arrangement of loading allowed to research into the effect of the beam’s span and the shear span-to-depth ratio on the load capacity and the fracture process in reinforced concrete beams without transverse reinforcement.

E XPERIMENTAL INVESTIGATION

he experimental investigation was performed on four beams: two slender beams: OI-1, OI-2 and two short beams: PI-1, PI-2. The beams had a rectangular cross-section of the width b = 0.12 m, the total height h = 0.25 m and the effective depth (depth measured from the compression edge to the level of longitudinal steel bars) d = 0.22 m. Two deformed steel bars of the diameter 18 mm were used as longitudinal reinforcement in the beams. The reinforcing steel was of RB500 category and it was characterized by the yield stress f y = 545 MPa and the tensile strength f t = 631 MPa. The ratio of longitudinal reinforcement was  = 1.8%. Transverse reinforcement was not used in the beams. The cross section of the beams is shown in Fig. 1.

Figure 1: Cross section of the beams.

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